Conventionally, for LTE (Long Term Evolution) or LTE-Advanced as a next generation mobile communication system, a heterogeneous network has been studied in order to improve system capacity and coverage. The heterogeneous network is a network in which a macrocell and a cell of a base station with low transmission power (hereinafter, described as a “picocell”) are arranged so as to coexist with each other. In such a network, when the macrocell and the picocell are operated at the same frequency, interference from the macrocell to the picocell becomes a problem. Namely, in a mobile station connected to a base station of the picocell (hereinafter, described as a “pico base station”), a signal from the pico base station is interfered with by a signal from a base station of the macrocell (hereinafter, described as a “macro base station”).
The inter-cell interference as described above influences the communication quality in each of physical channels (a control channel and a data channel). In particular, in a system in which a transmission timing of a subframe is synchronized between cells, the inter-cell interference may occur between the control channels and between the data channels. As a technology for reducing the inter-cell interference, there is a technology for shifting a transmission timing of a subframe in the pico base station with respect to a transmission timing of a subframe in the macro base station, in an OFDM (Orthogonal Frequency Division Multiplexing) symbol unit. In such a technology, a data channel of the macro base station that overlaps a control channel of the pico base station in the time domain as a result of the shift is overwritten (muting) with a null symbol with transmission power of zero.
Non Patent Literature 1: 3GPP TR 36.814 V9.0.0 (March 2010)
Non Patent Literature 2: 3GPP TS 36.211 V8.9.0 (December 2009)
Non Patent Literature 3: 3GPP TS 36.213 V8.8.0 (November 2009)
Non Patent Literature 4: 3GPP R1-103227
However, in the technology described above, while interference from the data channel of the macro base station to the control channel of the pico base station is reduced, there is a problem in that the reception characteristics of the data channel of the macro base station is degraded. Namely, because a null symbol is set in a resource that is muted to reduce the interference among resources of the data channel of the macro base station, the amount of data that the macro base station can transmit per unit time is reduced accordingly. The reduction in the amount of transmission data is a cause of degradation of the reception characteristics of the data channel.